Ambrose Kim Se-bak, also called ‘Gun-mi`, was born in 1761 in Seoul. His father was a translator. Immediately after the Catholic Church was introduced to Korea, he believed in God and became a Catholic. His adult name was `Eon-u`. Thomas Kim Beom-u, who died in exile around 1786, was a distant relative of his. After he came to believe in Catholicism, Ambrose Kim tried to teach the Catholic doctrine to his wife and children with great sincerity, but his family did not accept the new religion.

His wife was a violent woman and disturbed his Christian life with her outbursts, even insulting his religion. So he decided to leave his family and spent his time going around to teach the catechism to the people, and transcribing Catholic books. He then had the good fortune of meeting Father James Zhou Wen-mo who had come to Korea, and received the Sacraments from him.

Once in a while Ambrose Kim went to the mountain to pray and strengthen his faith life. He enjoyed teaching children and tried to be moderate in his eating habits. He was faithful to his prayer life. He never neglected to wake up in the middle of night to pray in silence.

When the Jeonghae Persecution broke out in 1827, Ambrose Kim realized that there was no way to escape, so he went to the Andong government office to surrender himself and confessed that he was a Catholic. Immediately he was taken to the chief official, who interrogated him to force him to report the whereabouts of his fellow Catholics and the religious books. But he said nothing. One month later, Ambrose Kim was transferred to Daegu, where he met Andrew Yi Jae-haeng, Andrew Kim Sa-geon and Andrew Pak Sa-ui. They encouraged and consoled one another keeping firm their faith in God.

They were often taken to the governor and severely tortured, but they endured all their trials with great patience and courage. The governor reported his crime to the Justice Ministry as follows:

"Kim Se-bak turned himself in and was imprisoned, but he never regretted what he had done in his life, though it meant he had to die."

Ambrose Kim signed the judicial document and waited for the day of his martyrdom. He decided to fast, as an offering to God and observed this practice faithfully, because he knew that his meals were provided from the taxes that were paid by the neighboring residents. When his companions wanted to follow his example and fast also, he advised them not to, saying, "It is like committing suicide." He then unwillingly yielded and started to eat again.

Completely worn out by repeated tortures and fasting, Ambrose Kim became gravely ill and life in prison became unbearable. Surrounded by his companions, he died in prison on December 3, 1828 (October 27, by the Lunar calendar). Ambrose Kim was 67 years old.

It is said that the Catholics lamented their friend`s death and revered his holy life, and his glorious ending in God`s grace.